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Full text of "Concreting in cold weather."

Concreting in Cold Weather 

Advantages 

Concrete work is now carried on regardless of season and tempera- 
ture. This is because the requirements leading to the success of con- 
crete work done when temperatures are low have become so generally 
known that contractors, cement products manufacturers, farmers and 
other users of concrete are now able to do concreting throughout 




Monolithic concrete silo in process of construction during the winter at the North 

Dakota Agricultural College, Fargo, North Dakota. Aggregates being heated over 

section of old smokestack or metal culvert pipe 



the year, thus finding profitable employment for time that might other- 
wise be idle. 

By observing some simple and easily applied rules for preparing 
concrete mixtures, then using a few simple means to protect the 
freshly placed concrete, the resulting work will be just as successful 
as though carried on during warmer weather. The farmer can keep 
his farm hands busy during spare time in the winter, making concrete 
fence posts, concrete block, small concrete watering troughs and tanks, 
and laying barn and other interior concrete floors ; thus his working 
capacity will be improved and his abilities as a producer of vital food- 
stuffs increased. 

Many concrete products plants take advantage of opportunities to 
keep their plants working throughout the year. A little expenditure of 
time is often all that would be necessary to fix one of the plant build- 
ings so that it could be made a comfortable workroom for carrying on 
the manufacture of a plant's specialty or specialties throughout the 
winter. 



CONCRETING IN COLD WEATHER 



Concrete work done when the average temperature is below a cer- 
tain point may cost a little more than the same kind of work done 



On the general run of contracting 



under the usual summer conditions 
this cost seldom runs more than 
10 per cent above that of work 
done in warm weather and fre- 
quently not more than 6 per cent 
— sometimes even less. Part of 
this extra expense comes from 
applying necessary protective 
measures, and part results from 
the lower efficiency of workmen 
through exposure to the cold. 
Some of the increased cost may 
be due to the added time neces- 
sary for the concrete to harden, 
which prevents such speedy 
progress of the work as would be 
possible in warm weather. 

Contractors have found that prospective builders are usually willing 
to pay any slight extra cost of work done in cold weather to obtain 
the benefit of having their buildings completed and ready for use at an 
earlier date. 





* 




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Pipe coils like this, laid over an open 

fire, can be used to heat water, flow 

being regulated so that water will heat 

while running through the coil 



P. 



Effect of Low Temperatures on Concrete Work 

Heat hastens the hardening of concrete ; cold delays it. The effect 
of cold becomes noticeable in this respect when temperatures are below 

50 degrees Fahren- 
heit, and becomes 
more marked with 
the lower tempera- 
tures. 

The general 
opinion is that freez- 
ing will not injure 
concrete that has 
first had an oppor- 
tunity to harden for 
at least 48 hours 
under favorable con- 
ditions. If, before 
early hardening has 
taken place, concrete 
is allowed to freeze 
and thaw at short 
intervals, it will be 
damaged. As a rule, concrete will not show any serious effects from 
having once been frozen if, after it thaws out, it is not again frozen 




Materials may be heated by thrusting steam pipes into 

them and covering the piles with canvas to retain the heat 

thus given 



CONCRETING IN COLD WEATHER 



until early hardening is complete. But it is far better to protect the 
Loncrete from freezing for from 48 hours to four or five days, depend- 
ing upon the degree of the cold, rather than to expose it to the possi- 
bility of freezing. If such protec- 
tion is given, no injury need be ^^ 
feared when the concrete is finally m 

DSed to freezing temperatures. 

Some of the requirements lead- 
ing to slk th concrete work 
done in cold weather are self- 
evident when one remembers the 
conditions under which concrete 
hardens and ga ength in 
warm weather. Warmth and 
moisture are necessary to the 
r hardening of concrete 
Any means that will cause both 
to be present, m 
' Lllarly during the period of eaily hardening, will 
lead to t: >rk done H such tunes, if ev< 
good allowed. 




Freshly placed concrete for roof of con- 
>il<>. pnttcctcd by cunt its COVtHmg 




£■#*"/' *- T 



Heating Materials 

1 !>bles or broken stone and mixing water a 
ai tned that more rapid i 

the mixing water and negle* 
Li insufl 

Warmth I the 

ttt f i (jm I - 

I Id in it ioi 
time — as long as 

i 
— if th< 

- d quickly 

mixii 

or n 

ways that will be 

Additional 

evel ; 1 1 1 
concrete masi at a 
hanges fa 
hir*^ ing place from 

chemical 




■nrrrtr ualk against poutbte 

J J'mn uith /»/«««'j ,,1 ihori boardi 
' «w ' being Noun a u 



CONCRETING IN COLD WEATHER 



of the cement and water. This also helps to keep up the temperature 
of the freshly placed concrete and thus aids to protect it from freezing. 
As cement forms only a relatively small bulk of a concrete mixture, it 
need not be heated, 
but it should be 
stored where it will 
be protected from 
dampness and ex- 
treme cold. 

Heating Water 

Mixing water is 
the easiest of the 
materials to heat. It 
can readily be heated 
to 150 degrees 
Fahrenheit, and kept 
at this temperature 
until used, by one of 
several methods. 
Two methods are in 
common use for heat- 
ing mixing water; 
one is to use live or 
exhaust steam from a steam plant, and the other is to heat the water 
in tanks or kettles over a fire. On large contracting jobs mixing water 
is usually heated by steam. If a steam engine is used to run the 




Work can be housed in by means of canvas tarpaulins 

and the enclosure kept at safe working temperature by 

salamanders 




Concrete sidewalks in business sections have often been made during cold weather 
by housing in as here shown and keeping the enclosure at proper temperature by 

using salamanders 



mixer, the exhaust steam is often allowed to discharge into a water 
tank that is a fixture on the mixer. This arrangement is satisfactory, 
but does not heat as rapidly as live steam. 



CONCRETING IN COLD WEATHER 



Live steam, which is steam under pressure, furnishes more heat 
where considerable quantities of water are required at regular inter- 
vals. When live steam is used and the water has been heated as 
required, its temperature can readily be kept at the desired point by 
a regulating valve that will admit only enough steam to the water to 
keep it hot. An old steam boiler that is no longer safe for carrying 
high steam pressures may sometimes be used as a source of steam 
supply, since a boiler pressure of 25 pounds is sufficient for the purpose. 

On small jobs a tank or large kettle supported above a fire may 
supply all the heated water that is needed. Coils of pipe similar to 
steam radiator coils have been supported above a fire and water 
allowed to flow slowly through the coils and into a barrel, the water 
being heated as it passed through the coils. In such a case also after 
the required amount of water has been heated, it can be kept at the 
desired temperature by allowing no more water to pass through the 
coil than can be converted into steam, this being discharged into the 
barrel. 




Aggregates being heated by thrusting steam pipes into the material as received 

loaded on cars 

Heating Sand and Pebbles or Broken Stone 

Unless sand, pebbles and broken stone are stored indoors during the 
winter, they are certain to contain frost, and sometimes lumps of snow 
and ice. Frozen materials should not be used in concrete mixtures. 
They not only chill the concrete, but prevent thorough mixing. Sand 
and pebbles or broken stone should be heated. A temperature not 
exceeding 150 degrees Fahrenheit will generally prove sufficient. Too 
much heat will injure some kinds of sand and pebbles or broken stone, 
particularly limestone. 



CONCRETING IN COLD WEATHER 




Complete protection afforded by enclosing the work by use of tarpaulins 

On small jobs these materials are usually warmed by piling them 
over and around sheet iron cylinders, such as an old smokestack, a 
section of old iron sewer or culvert pipe, or an old steam boiler. A 




"Working under summer conditions" on the concrete building of the Robertson-Cataract 
Electric Co., Buffalo, N. Y.. February, 1916. Usually such complete methods of housing 

in are not required 



8 



CONCRETING IN COLD WEATHER 



fire is built within and the materials to be heated piled around and 
upon this "stove." Sometimes a stove is built by using concrete block 
for a foundation and covering with a piece of sheet steel such as boiler 
plate. It is necessary to turn or rake over the materials frequently so 
that those nearest the fire will not become too hot and thus possibly 
injured, while at the outside and edges of the pile they may not be 
warmed. 

Separate stoves are best for heating sand and pebbles, although 
sometimes a pipe stove may be long enough so that sand can be piled at 
one end and pebbles or broken stone at the other. Care should be used 




Open fire pots or salamanders like the one shown here are generally used to provide heat 
necessary to keep enclosures warm enough to prevent concrete from freezing 



to keep the two materials separate, otherwise when taking them from 
the pile to proportion a batch of concrete, some batch is likely to be 
improperly proportioned because the sand and pebbles became mixed 
before measuring. 

Heating sand and pebbles or broken stone by steam has advantages 
over other ways. They may be piled directly on steam-heated pipe 
coils or the piles may be covered with tarpaulins and steam applied 
directly to the materials. The tarpaulins act to house in the piles and 
thus to hold the heat. With a steady supply of steam this method of 
heating is quite effective. The pipes used are closed at one end and 
perforated along their lower side by numbers of very small holes. The 
other end of the pipe is connected to the source of steam supply by 
means of steam hose. The pipes are then stuck into the piles of 
materials and steam turned on. 

While cold weather concreting is in progress, piles of sand and 
pebbles or broken stone exposed to the weather should be kept covered 



M, 



CONCRETING IN COLD WEATHER 



with tarpaulins to prevent the materials from becoming water-soaked 
and possibly frozen solid if the temperature should drop suddenly. 

Use of Salt in Mixing Water 

Water containing common salt, calcium chloride (chloride of lime) 
and a number of other chemicals will not freeze at the same tempera- 
ture as water which contains none of these substances. For this rea- 
son, it was common when concrete work was first done in cold weather, 
to add salt to the mixing water to prevent the concrete from freezing! 
As not more than 10 per cent of salt can safely be used without danger 




Newly laid floor housed in by building a scantling frame and covering with 
canvas. The enclosure is heated by salamanders kept burning beneath this 

covering 



of affecting the final strength of the concrete and as such a quantity of 
salt gives protection only against a possible drop of temperature of 10 
degrees below freezing, the use of salt is not effective when cold is 
extreme. Besides, salt does not accomplish the one thing most desir- 
able. It delays instead of hastens the hardening of the concrete. Salt 
is considered objectionable in reinforced concrete because it may 
corrode the reinforcing steel. Salt should not be used where the 
appearance of the finished work would be spoiled by the whitish 
deposit that may later appear on the surface. This deposit is com- 
monly referred to as efflorescence and may be expected on work in 
which salt has been used. 

In general, calcium chloride (chloride of lime) is also objectionable 
for reasons similar to those mentioned for salt, although experiments 
conducted by the United States Bureau of Standards indicate that 
there may be a possible advantage in using it in some cases, because 
a 4 per cent solution in water seems to hasten the hardening of con- 
crete. The use of calcium chloride is said to increase the cost of 
concrete work from 12 to 15 cents per cubic yard. 



10 



CONCRETING IN COLD WEATHER 



Heating Forms 

Before placing concrete in cold weather forms should be thoroughly 
cleaned of snow, ice or particles of frozen concrete. Metal forms 
should always be heated. In extremely cold weather wood forms also 
should be heated. Turning a jet of steam against form faces is best 
when available. 




Reinforced concrete construction on the West 9th Street terminal, Cleveland, Ohio, 
during the winter of 1916-17 



Protection to Be Given 

In the following paragraphs a number of ways of protecting con- 
crete work done in cold weather will be described. Usually no one 
of these methods or ways is used alone. Generally two or more of 
them are combined. 

After forms have been cleaned of ice, snow and any particles of 
frozen concrete, and have been warmed, the concrete mixture should be 
placed immediately so that none of the warmth given to it by the 
heated materials will be lost. All of the work should be done as 
quickly as possible. 

Thin floor slabs, beams, columns, sidewalks, feeding floors, barn- 
yard pavements and similar classes of work have a large surface area 
compared with their volume ; therefore, more careful protection must 
be given to such work than to foundations, abutments and other mass 
construction where the excavation or the bulk of the mass and heavy 
forms give part of the required protection. Floors are usually pro- 
tected by a covering of hay or straw. Building paper or canvas should 



CONCRETING IN COLD WEATHER 



11 



first be laid over the concrete, then from 6 to 12 inches of straw, 
depending upon the temperature to be protected against. If the work 
is out of doors the covering should be weighted down with short 
boards to prevent it from being blown away. Sidewalks, feeding 
floors and road and street pavements must receive extra care. Some- 
times walks in business districts are housed in by means of a canvas- 
covered frame and the enclosure kept warm by steam or open coke- 
burning stove pots, commonly spoken of as salamanders. 




Sometimes an old steam boiler not safe for usual working pressures can be used to 
generate steam sufficient to warm mixing water on the job 



When forms are tight and made of heavy material, mass work may 
require no other protection than covering the concrete exposed at the 
top. This protection can be given by a layer of hay or straw, while 
vertical faces may be given additional protection besides that given by 
the forms by building a rough lattice work of strips 10 or 12 inches 
from the outside face of forms and filling in between lattice and forms 
with straw or manure. Such extreme measures are usually required 
only when the cold is very severe. 

If manure is used as a covering, it should never be placed directly 
upon the fresh concrete. It is not only likely to stain the work, but 
may injure the surface by causing a slight pitting or scaling. This is 
probably due to the fact that sometimes nitric acid is formed when the 
manure rots and this chemical is probably the substance that has 
caused injury to concrete surfaces protected by manure covering, in 
those cases observed in the past. 



12 



CONCRETING IN COLD WEATHER 



Foundations can easily be protected because the greater portion of 
the work is in an excavation. Forms, or earth walls of the trench give 
enough protection to the sides of the work if the cold is only moderate. 
There remains nothing but the top surface to be covered. 

Barn and stable floors built during winter should be laid in such 
sections that a portion of the old floors may be used while concreting 
is in progress. This is necessary because of the longer time that con- 
crete requires for hardening in cold weather to be safe for use. 




Reinforced concrete fish packing building at Portland, Me,, during the winter 

weather. Concrete work was made possible by observing all precautions described 

in this booklet and by housing in the work as shown with canvas 

For such indoor work little additional protection is needed besides 
that given by the enclosing structure. Temperature may be kept as 
desired by oil stoves. Do not have a dry heat. Pans of water over 
salamanders or stoves will furnish sufficient moisture. Care should 
be taken, however, to prevent the possibility of fire. This also applies 
where salamanders or open coke-burning stoves are used to supply 
heat. It is a wise precaution always to have an attendant on the job 
as a measure of safety against the spread of fire. 



Removing Forms 

Although too early removal of forms is to be avoided regardless of 
season, this statement applies with great force to work done during 
cold weather. Especially is this true of concrete walls, roofs, and 
overhead floors which are intended to carry loads other than their own 
weight. Forms should be left in place until it is absolutely certain 
that the concrete has become strong enough to be safe. Frozen con- 
crete often has the appearance of thoroughly hardened concrete. If 
struck with a hammer it will ring just like hardened concrete. The 
work should be examined carefully before forms are removed. A 
single section of the forms or part of a section may be removed to 
expose the concrete, then the flame from a plumber's blow torch, a jet 
of steam or hot water may be directed against the concrete surface. 



CONCRETING IN COLD WEATHER 



13 



If merely frozen the heat will thaw the water in the concrete, thus 
showing the condition of the work. 

Cold Weather Concrete Work on the Farm 

There is much concrete work on the farm that may be carried on 
during cold weather. Farm hands may thus be kept at work when 
they might otherwise be idle. Concrete block, fence posts, small 
watering and feeding troughs can be made indoors. 

A convenient room for carrying on cold weather concrete work 
indoors can usually be arranged by fixing up some portion of a shed, 
barn or cellar. Sand and pebbles should be brought into the work- 
room and stored until desired for use. The workroom temperature 
should never be lower than 50 degrees Fahrenheit. If the materials 
are stored in such a temperature, frost or frozen lumps of material 
that may have been in them will disappear if the piles are well raked 
over occasionally. Materials containing frost or frozen lumps must 
not be used in concrete mixtures. If the workroom is not large enough 








Concrete construction at Pabos, Quebec, carried on during severe winter weather. 
This work was housed in as it progressed, and usual precautions used to pre- 
vent freezing 

to store a considerable quantity of materials and they must therefore 
be brought indoors as required for use, some means for heating them 
must be arranged. 

Care must be taken to prevent concrete block, fence posts and 
similar products from freezing during the first two or three days after 
made. They should be stored for a long time before being used, pref- 
erably until spring. 

Cold Weather Highway Work 

It is sometimes necessary to complete a job of concrete street or 
road paving when temperatures may drop below freezing, and on such 
work caution should be taken to avoid any possibility of damage to the 
concrete by frost. 



14 



CONCRETING IN COLD WEATHER 



Concrete should not be placed on a frozen subgrade. Methods to 
be followed in combating the injurious effects of cold weather may 
be grouped under the following headings : 

(a) Application of artificial heat to materials or finished work, and 
means of preventing the dissipation of heat developed during the set- 
ting of the cement. (Heating of water or aggregates; heating fresh 
concrete by steam lines; the use of covering, etc.) 

(b) Use of chemical compounds which will lower freezing point 
of mixing water, or hasten setting of the cement. 

Special care must be taken to avoid the use of lumps of frozen 
aggregate. This is generally called to attention in the specifications. 




Framework used for supporting covering to protect concrete pavement laid during cold 

weather near Quantico, Va. 

On account of the frequent moving of equipment, heating of aggre- 
gates is not always practicable in road work, although this can be done 
in other kinds of concrete construction. 

If a source of steam supply is available, aggregate may be heated 
by inserting steam pipes carrying live steam into the piles. This 
heating will be greatly facilitated by covering the piles with canvas. 

Desirable results can be obtained at little expense by heating the 
mixing water. This can best be accomplished by inserting an im- 
provised steam coil in the water line near the mixer. The water coil 
may be heated by a wood or coal fire. It is not necessary that the 
water be extremely hot, as it will accomplish a useful purpose if this 



CONCRETING IN COLD WEATHER 



15 



method serves to remove only the chill from the aggregate and impart 
some heat to the fresh concrete. Satisfactory heaters for this purpose 
are on the market. 

In the event of an extreme drop in temperature, pipe lines supplied 
with live steam may be carried under the canvas to protect the fresh 
concrete from freezing. If the concrete has partly hardened, protec- 
tion may be provided by covering with straw. 

A 1-inch layer of sawdust with a canvas overtop has been found 
very satisfactory where the temperature does not drop more than three 
or four degrees below freezing. Hay or straw used as a covering, 
with canvas on top, will serve the same purpose. It is important that 
where this is used the material be lightly forked onto the road so as 
to retain as much air as possible, which is the heat retaining medium. 




Heating aggregates used in concrete road work done near Quantico, Va., during the 

winter of 1917-18 



Cold Weather Concrete Work 
For Concrete Products Plants 

In general, the recommendations already given for doing concrete 
work in cold weather apply to the manufacture of concrete products 
at commercial plants. Many such plants have buildings that do not 
permit the operation of the plant twelve months a year. In most cases 
they could be fixed up at little expense and the plant be profitably 
operated all the year. 



16 



CONCRETING IN COLD WEATHER 



Workrooms and hardening rooms or chambers should be so ar- 
ranged that drafts of cold air will be prevented from striking the 
freshly-made concrete products. The workroom temperature should 
be kept above 50 degrees Fahrenheit. 

Modern plants harden their concrete products by steam. This is 
a great advantage at any time of year, but particularly so in cold 
weather. 

In all cold weather concrete 
work the size of concrete batches 
mixed should be so regulated 
that each batch may be used 
quickly in the molds or forms. 
The mixed concrete should not 
be exposed before placing so that 
it may lose some of the warmth 
given it by heated materials. 




Construction view taken December 31, 1915, while cold weather concrete work was in 
progress on the building of the Sperry Gyroscope, New York. Turner Construction Co., 

New York, contractors 



Of Interest to the Contractor 

Concrete contractors who are prepared by experience and equip- 
ment to keep their forces employed during cold weather know the 
profits resulting from thus lengthening their working season. Their 
equipment is usually such that it is easy for them to apply the precau- 
tions that have been described in this booklet as necessary. One large 
construction company in the East makes cold weather concreting 
almost a specialty. This, however, should not cause contractors in 
general to look at this class of work as one in which they also should 
specialize. Long experience with cold weather concreting is neces- 
sary for success on large jobs. 

The last edition of the Building Code Recommended by the 
National Board of Fire Underwriters, New York, devotes some space 
to measures that are recommended in connection with cold weather 



CONCRETING IN COLD WEATHER 



17 



concreting. Among other things, this code suggests that "when con- 
crete has been deposited while the outside temperature was above 40 
degrees Fahrenheit with a rising temperature, " ample supports be 
left to carry the construction until it is undoubtedly safe to remove 
them. This code further recommends that "a special permit should 
be obtained for removal of forms from concrete deposited when the 
outside temperature was below 32 degrees Fahrenheit and the number 
of days required should be increased in proportion to the amount 
of time the temperature remained below 32 degrees Fahrenheit after 
the concrete was deposited." 




«ULURD MACHINE TIlUi. 
BRIDGEPORT, CONN. 

tNER CONSTRUCTION CO.. 
NEW YORK CITY 
DATE MAR. ». 191ft 



An example of winter concrete work carried on by the Turner Construction Co., New 
York, showing protection to the interior of one story white the floor is being concreted 

For the contractor not thoroughly experienced in cold weather 
concrete work it is recommended that, when the average temperature 
for the day is between a minimum of 40 and a maximum of 50 degrees 
Fahrenheit, the building in or on which work is being carried on 
should be enclosed. When the average temperature is below 40 de- 
grees and above 35 degrees Fahrenheit, the materials should be heated. 
When the average temperature falls below 35 degrees Fahrenheit, the 
building should be heated by salamanders or similar means so that the 
interior temperature surrounding the concrete work will always be 
higher than 40 degrees. 



18 



CONCRETING IN COLD WEATHER 



Occasionally it is necessary for the contractor to make some provi- 
sion on the job for the comfort of his workmen. Shelters or wind 
shields have been built around benches where carpenters were building 
forms, as well as around the concrete mixer to protect the men. Where 
excavating is going on in the open, it is best to have a small shanty 
with a good fire where the men can warm themselves occasionally. 
Other means of furnishing reasonable comfort for men working under 
unfavorable temperature conditions will suggest themselves to the 
experienced contractor. 

Facts to Remember 

REMEMBER that 
during the first few 
days following the 
placing of concrete, 
alternate freezing and 
thawing at compara- 
tively short intervals 
will damage it. 

REMEMBER that 
protecting the con- 
crete against possibil- 
ity of freezing is best, 
even though concrete 
which freezes before 
early hardening has 
been completed may 
not be permanently 
injured, if after thaw- 
ing out it is not again 
exposed to freezing 
until hardened. 




Concrete grain bins built during freezing weather by 
using canvas covering to retain heat given by salaman- 
ders kept burning inside the bins. On this particular 
job concrete was mixed by hand in structure beneath 
this protection 



REMEMBER that it is necessary to so mix, place and protect the 
concrete that early hardening will be complete before the work is 
exposed to freezing temperatures. 

REMEMBER that to do this: 

(1) Sand and pebbles or broken stone used must be free from 
frost or lumps of frozen materials. 

(2) If these materials contain frost or frozen lumps they must 
be thawed out before using. 

(3) As cement forms but a relatively small bulk of the materials 
in any batch of concrete, it need not be heated. 

(4) Mixing water should always be heated. 

REMEMBER that although adding common salt to mixing water 
will prevent freezing of fresh concrete until it has had time to harden, 
there is a limit to the quantity of salt which may be added if the final 
strength of the concrete is not to be affected. Salt simply lowers the 
freezing point of the mixing water; it does not supply what is most 



CONCRETING IN COLD WEATHER 



19 



needed-heat and warmth. It delays, instead of hastens, the harden- 
ing of the concrete. 

REMEMBER that sand and pebbles or broken stone and mixing 
water must be heated so that the concrete when placed shall have 1 
temperature of from 75 to 80 degrees. 

REMEMBER that some sands are injured by too much heat The 
same applies to certain varieties of pebbles and broken stone A 
temperature not exceeding 150 degrees Fahrenheit will generally prove 
most satisfactory. J r 

REMEMBER to place concrete immediately after mixing so that 
none of the heat will be lost before placing in the forms. 

REMEMBER to warm metal forms and reinforcing before placing 
concrete. Be careful to remove ice and snow and frozen concrete 
remaining on the forms from preceding work. Forms can be warmed 
by turning a jet of steam against them or by wetting with hot water. 

REMEMBER that even though materials have been heated and 
the concrete placed immediately after mixing, it will lose much of its 
neat it not protected from low temperatures, at once. 

REMEMBER, therefore, to protect the concrete immediately after 
placing. Canvas covering, sheathing, housing-in the work, or hay or 
straw properly applied will furnish the required protection for differ- 
ent jobs. In addition to these means, small oil or coke-burning stoves 
or salamanders may be used in enclosed structures. Guard against 

REMEMBER that temperatures which may not be low enoueh to 
freeze the concrete may, nevertheless, delay its hardening for a con- 
siderable time. Do not expect concrete placed when the temperature 
is low and remains low for some time afterward to be safe for use as 
soon as though placed during warmer weather. 

REMEMBER that if concreting is unavoidably delayed or inter- 
rupted the work should be covered until concreting is again begun. 

REMEMBER to cover and protect any section of the work as soon 
as completed. In severe cold weather, continue this protection for at 
least five days. 

REMEMBER that forms must not be removed from the concrete 
work too early. This applies to any concrete work, regardless of 
season, but is particularly important with work done during cold 
weather. b 

REMEMBER that frozen concrete sometimes very closely re- 
sembles concrete that has thoroughly hardened. When frozen con- 
crete is struck with a hammer it will often ring like properly hardened 
concrete. Before removing forms, examine the work carefully to see 
whether it has hardened or simply frozen. To determine this, remove 
one board from some section of a form, pour hot water on the concrete 
or turn the flame of a plumber's blow torch or a jet of steam under 
pressure against the concrete. If the concrete is frozen, the heat will 
soften it by thawing the water contained in it. 

REMEMBER— SAFETY FIRST. 



y= 



When You Build 
USE CONCRETE 



Whether your problem in- 
volves a barn or a house, 
a factory or warehouse, 
grain elevator or cold stor- 
age plant, school or hos- 
pital — any structure you 
can think of — concrete rep- 
resents greatest ultimate 
economy. 

Help stop the criminal waste 
caused by impermanent construc- 
tion. Concrete beats fire, flood, 
rats, rot, waste, disease. Concrete 
consumes nothing. It adds to 
the permanent wealth of the 
nation. It means a strong, per- 
manent second line of defense. 

Are You a Waster or a Warrior? 



Portland Cement Association 

OFFICES AT 

Atlanta Detroit Kansas City New York Salt Lake City 

Chicago Helena Milwaukee Parkersburg San Francisco 

Dallas Indianapolis Minneapolis Pittsburgh Seattle 
Denver Washington 



"WAR SAVINGS STAMPS 

I13UED BY THE 

U KITED STATES 
GOVERNMENT 



Concrete for Economy — Concrete for Permanence 



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